1. Field of the Invention
The present invention relates to a magnetic disc apparatus, a magnetic head, and a production method thereof and in particular, to a magnetic head in which a recording/reproduction element is mounted on a magnetic head slider via a piezoelectric element so that the position of the recording/reproduction element can be adjusted in job mode by displacement of the piezoelectric element, and its production method, and to a magnetic disc apparatus using the magnetic head, and its production method.
2. Description of the Related Art
In a magnetic disc apparatus, recording density can be increased by increasing the recording density (linear recording density) of the magnetic disc rotation direction and the recording density (track density) of the magnetic disc radial direction.
In order to increase linear recording density, it is necessary to reduce the spacing between the magnetic head recording/reproduction element and the magnetic disc. In a conventional magnetic disc apparatus using a float type slider, spacing is reduced by weakening the floating power of the float type slider.
FIG. 10 is a perspective view of a conventional magnetic head (conventional float type magnetic head) using a float type slider. FIG. 10 shows the magnetic head with its float surface (to face a magnetic disc) upward. The reference symbol 20 denotes a slider, 13 denotes a float plane, and 21 denotes a recording/reproduction element.
When floating power of a float type slider is weakened, spacing can follow a greater waviness of the magnetic disc. However, when floating power is weakened, spacing cannot follow a surface configuration (wavelength from micrometers to millimeters, and frequency from several tens of kHz to several hundreds of kHz) of a dimension similar to that of the magnetic head slider. Accordingly, the spacing fluctuates. Moreover, the magnetic head may be brought into contact with the magnetic disc, causing friction.
Moreover, in a conventional magnetic disc apparatus, in order to increase track density, for example, a rotary actuator is used to perform track positioning by driving a head gimbal assembly consisting of a support spring and a magnetic head slider, in a magnetic disc radial direction.
However, in the case of a head gimbal assembly, the magnetic head position is to be controlled via a structure of a low rigidity and low resonance frequency such as a gimbal spring from a position far away from the magnetic head. Accordingly, it is difficult to perform track positioning with high speed and high accuracy.
Moreover, in the case of a recording/reproduction element in contact with a magnetic disc, the magnetic head is moved against friction between the recording/reproduction element and the magnetic disc. Accordingly, it becomes more difficult to perform track positioning with high accuracy.
Thus, in the conventional magnetic disc apparatus, it has been difficult to simultaneously improve linear recording density and track density. For improving recording density, various suggestions have been made. Firstly, conventional techniques for improving linear recording density will be shown.
Tribology and Mechanics of Magnetic Storage System, Volume 7, 1990, pp 158–164 [1] discloses a technique for reducing spacing by burying a piezoelectric element expanding and contracting in parallel to the drive electric field, into the back of a float type magnetic head slider and applying an electric field to this piezoelectric element.
FIG. 11 is a perspective view of a conventional magnetic head (magnetic head slider) in which a piezoelectric element is buried into the back of a float type magnetic head slider. FIG. 12 explains the operation of a conventional magnetic head (magnetic head slider) in which a piezoelectric element is buried into the back of a float type magnetic head slider. In FIG. 11, the reference symbol 20 denotes a slider, 21 denotes a recording/reproduction element, 22 denotes a layered piezoelectric element, and 23 denotes electrodes. In FIG. 12, the reference symbol 30 denotes a magnetic disc. The reference symbol 24a indicates a displacement direction of the piezoelectric element, 24b indicates a displacement direction of the recording/reproduction element caused by the displacement of the piezoelectric element, and 17 indicates the spacing direction.
Japanese Patent Publication 1-107385 [2] discloses a magnetic recording apparatus in which a displacement sensor measures the distance between a magnetic recording medium and a magnetic head and an actuator is driven so as to maintain the distance constant, so that the interval between the medium and the head is reduced. This magnetic recording apparatus is constituted as follows. The interval between the magnetic recording medium and the magnetic head is measured by an intensity change of the return light emitted from a light reflection intensity type displacement meter through an optical fiber and reflected from the medium surface. The magnetic head uses a piezoelectric actuator driven by a servo circuit and an amplifier according to a displacement fluctuation signal from the light reflection intensity type displacement meter, and maintains a constant distance from the surface of the magnetic recording medium. Thus, by measuring the distance between the magnetic recording medium and the magnetic head using a displacement sensor so that the distance is maintained constant by driving the actuator attached to the magnetic head, it is possible to maintain a very small interval between the magnetic recording medium and the magnetic head as a non-contact state or contact state with a very small weight.
Japanese Patent Publication 7-235157 [3] discloses a magnetic disc apparatus in which the distance between the magnetic head and the magnetic disc is measured from time to time and maintained constant while performing a signal recording/reproduction so that a floating margin is reduced and recording is enabled with a smaller floating amount. This magnetic disc apparatus is constituted as follows. When the magnetic disc apparatus is started and the magnetic disc is rotated at a comparatively low speed, the magnetic head floats over the magnetic disc surface and reads a signal recorded, with the reproduction element mounted, while traveling in a floating state. From strength of this signal, a detailed floating amount fluctuation is read and a control signal is transmitted to the piezoelectric element. The piezoelectric element, upon reception of the control signal, expands and contracts in the longitudinal direction so as to raise and lower the recording element and the reproduction element according to the unevenness of the surface so as to maintain a predetermined distance from the surface and maintain a float amount constant. Accordingly, it is possible to obtain a magnetic disc apparatus having a smaller float amount and a higher recording density. Moreover, it is possible to prevent contact between the magnetic head and the magnetic disc.
Next, conventional techniques for improving mainly the track density will be shown.
Although the document name [4] is unknown, there has been suggested a technique to drive a support spring supporting a magnetic head slider by an electromagnetic actuator in order to increase track density.
The Japan Society of Mechanical Engineers, proceedings (4), No. 98-1, 1998, pp 208–209 [5] describes a technique to drive an entire magnetic head slider by a piezoelectric element beam.
The Japan Society of Mechanical Engineers, proceedings (4), No. 98-1, 1998, pp 210–211 [6] describes a technique to drive a recording/reproduction element by an electrostatic actuator provided at the back end of a slider.
Japanese Patent Publication 3-245315[7] discloses a head slider on which a drive member is provided for changing the position of a transducer in the positioning direction (track width direction), so as to perform positioning with high speed and high accuracy. This head slider is constituted as follows. The drive member is a piezoelectric element which changes its size in a direction perpendicular to the positioning direction. Furthermore, a conversion mechanism is provided on the slider for converting the piezoelectric element size change into a displacement amount of the transducer in the positioning direction. The conversion mechanism converts a deformation amount of the drive member in a direction perpendicular to the positioning direction of the transducer (track width direction) into a displacement amount in the positioning direction of the transducer. Thus, use of the drive member increases the degree of freedom.
Japanese Patent Publication 6-176336 [8] discloses a magnetic recording/reproduction apparatus in which data parallel transfer is enabled, high speed data transfer is realized, and a servo can be operated for each of the recording/reproduction elements, increasing positioning accuracy and track density. This magnetic recording/reproduction apparatus is constituted as follows. Rail members constituting the slider are connected to a piezoelectric element and the rail interval is made variable. By using a plurality of these configurations, a multi-element slider is realized. In this apparatus, for each of the recording/reproduction elements, there is provided a recording/reproduction circuit, so that recording/reproduction is performed simultaneously. By controlling the piezoelectric element for the rail interval, it is possible to accommodate variable track densities.
Japanese Patent Publication 7-73619 [9] discloses a magnetic head and a magnetic recording/reproduction apparatus which performs tracking control of the magnetic head. The magnetic head is intended for enlarging a data region in a recording medium and increasing accuracy of off track control. This magnetic head and the magnetic recording/reproduction apparatus using this magnetic head are constituted as follows. A magnetic head is constituted by providing a piezoelectric element at a cut-off portion of a slider for moving a movable block having a thin film head in the magnetic disc radial direction by electrostrictive displacement. The piezoelectric element is driven according to read data error detection so as to control the off track. Thus, servo information can be removed from a data region of the recording medium.
FIG. 11 shows a magnetic head in which a piezoelectric element expanding and contracting in parallel to the drive electric field is buried in the back of a floating type magnetic head slider. By applying an electric field to this piezoelectric element, spacing is reduced. With this magnetic head, as shown in FIG. 12, the recording/reproduction element may be inclined and the recording/reproduction element may not be at the lower most point of the magnetic head slider. In other words, there may arise a clearance between the recording/reproduction element and a magnetic disc. Moreover, in this technique, the piezoelectric element expands and contracts too much in the magnetic disc rotation direction and time fluctuation (jitter) of a recording/reproduction signal may become remarkable.
The technique described in Document [2], i.e., the technique to drive a magnetic head into the spacing direction by a piezoelectric actuator has a problem that it is difficult to follow the magnetic disc swell (amplitude of 1 to 10 micrometers, wavelength of several tens to hundreds of mm, and frequency of several tens to hundreds of Hz) only by the piezoelectric actuator.
The magnetic head used in the magnetic disc apparatus described in Document [3] has a structure that a recording/reproduction element is attached downward via a piezoelectric element at the rear portion of the magnetic head slider. Accordingly, a piezoelectric element and a recording/reproduction element are mounted on each magnetic head slider, which is not appropriate for mass production of magnetic heads.
The technique to drive the support spring supporting a magnetic head slider, by an electromagnetic actuator, and the technique to drive the entire magnetic head slider by a piezoelectric element beam have a problem that resonance frequency is too low. Moreover, since the drive source is apart from the recording/reproduction element, there is a problem that there arises a delay of a reproduction signal used for position detection information.
The technique to drive a recording/reproduction element by an electrostatic actuator provided at the rear end of the slider has a problem that a flexible spring structure is used and resonance frequency is too low, and because the drive force is small, it is difficult to drive the recording/reproduction element at a high speed.
The head slider described in Document [7] can perform positioning in the track direction but cannot control the spacing direction.
The magnetic recording/reproduction apparatus described in Document [8] can perform a multi-element simultaneous tracking but cannot perform control in the spacing direction.
The magnetic head described in Document [9] has a structure that a thin film head is attached via a piezoelectric element at a cut-off portion formed in the slider. Accordingly, it is necessary to mount a piezoelectric element and a recording/reproduction element for each slider, which is not appropriate for mass production of magnetic heads.
Moreover, the minimum spacing is the state that a recording/reproduction element of the magnetic head is in contact with the surface of a magnetic disc. However, with the conventional techniques, it is difficult to increase the track positioning accuracy in such a minimum spacing state.